1. Field of the Invention
This invention relates to a new process for preparing propylene glycol monoalkyl ethers. More particularly, the invention relates to an improved process for preparing propylene glycol monoalkyl ethers from acetaldehyde, an alkanol and syngas using a new catalyst system.
Specifically, the invention provides a new and improved process for preparing in good yield propylene glycol monoalkyl ethers from acetaldehyde and an alkanol (or reacting an acetal) with carbon monoxide and hydrogen in the presence of a catalyst comprising a cobalt-containing compound and a cocatalyst comprising a member of the group consisting of rhodium-containing compounds, ruthenium-containing compounds and nickel-containing compounds, and heating the resulting mixture at moderate temperatures and pressures for sufficient time to produce the desired glycol monoalkyl ether, and then recovering the same from the reaction mixture.
2. Prior Art
Glycol monoalkyl ethers have a wide variety of applications as solvents and reaction media. In the prior art, the glycol monoalkyl ethers are commercially produced by preparing an olefin oxide from an olefin and adding a suitable alcohol thereto. This method is based on the use of an olefin which is a petroleum product which is becoming costly to obtain. As a result, industry is seeking a new method for producing glycol monoalkyl ethers from starting materials other than olefins.
One proposed method is the reaction of an acetal with carbon monoxide and hydrogen in the presence of a cobalt carbonyl catalyst (West German Pat. Nos. 875,802 and 890,945). This method, however, suffers from the disadvantage of low selectivity of the glycol monoalkyl ether. U.S. Pat. No. 4,071,568 proposes the production of the glycol monoalkyl ethers by the same method using a catalyst made up of a cobalt compound and certain phosphorus or nitrogen-containing ligands. This method also suffers from the disadvantage of low yields of the desired glycol monoalkyl ether and the need to use relatively high pressures of the syngas.
It is an object of the invention, therefore, to provide a new process for preparing propylene glycol monoalkyl ethers. It is a further object to provide a new and improved method for preparing propylene glycol monoalkyl ethers from acetaldehyde, alcohols and syngas using a new catalyst system. It is a further object to provide a new process for preparing propylene glycol monoalkyl ethers from acetaldehyde, an alkanol and syngas which operates at moderate temperatures and moderate pressures. Other objects and advantages of the invention will be apparent from the following detailed description thereof.